More and more people are now becoming aware of the problem that plastic poses for a sustainable way of life. But one important thing to understand is that not all plastic was created equal. Many are concerned by the carbon and other environmental costs of using a polytunnel to grow food year round. But calculations show that a well-utilised polytunnel can easily be of ecological benefit rather than of ecological cost.
Calculations regarding the materials used, their transportation and use, alongside a calculation of the potential reduction in carbon emissions and other forms of pollution over the lifetime of the structure, can show that the ecological benefits of a polytunnel can frequently outweigh the ecological costs.
The Ecological Cost of a Polytunnel
As with almost any item that we buy, polytunnels do have an ecological cost. As with any item, calculating the ecological cost of the product involves looking at the entire life cycle. Of course, a polytunnel will have a carbon cost at the point of manufacture, and there will also be a carbon cost associated with transporting the polytunnel to your site.
The Carbon Cost of a Polytunnel Cover
In order to calculate the carbon cost of a polytunnel, one must take into account its feedstock (the material required to create the plastic in the first place), the energy required for its manufacture, and the carbon cost involved in transporting it from where it was made to its final destination.
The carbon inherent in the material itself (plastic is derived from fossil fuels) is sequestered (trapped) within the product during its lifetime, and would only be re-released to the atmosphere if the plastic is burned. It is important to note that a polytunnel cover can and should be recycled at the end of its useful life, thereby preventing this carbon from being emitted to the atmosphere.
When it comes to creating the plastic cover, however, there is of course a heavy carbon cost involved. As a general guide, 3kg of CO2 emissions are required to manufacture 1kg of plastic. Using this guide, you can easily work out how much CO2 was released in the manufacture of your polytunnel cover, based on its weight.
Further to this, calculating the carbon cost of the polytunnel cover also involves taking into account the CO2 emissions involved in getting the plastic cover to your site from its point of manufacture. The equation used to estimate the carbon cost of freight transportation is the weight of the plastic x the distance in km x gCO2/tonne-km. The average road transport CO2 emission factor in Europe is 62g CO2/tonne-km. For rail freight, this drops to 22g CO2/ tonne-km. Obviously, this is a rough figure, and can vary, but can give a realistic idea of the rough carbon cost of the transportation of a product in terms of the carbon it releases. 1 Fortunately, significant measures are being taken in Europe to reduce the CO2 emissions of transportation to meet current targets, and fuel-efficiency measures and the introduction of more and more electric vehicles is set to reduce this cost further in the coming years.
The Carbon Cost of a Polytunnel Frame
Of course, calculating the carbon cost of a new polytunnel involves not only materials calculations for the cover, but also for the metal frame. The rule of thumb to use for this calculation is that 1.83kg of CO2 is released for each 1kg of steel produced. In addition to this, again, the transportation can be calculated using the formula given above.
Interestingly, most polytunnel purchasers will find that the carbon emissions released to acquire the metal frame will be much higher than that emitted in pursuit of the plastic cover (the part about which most new polytunnel owners are most concerned.) The weight of this structure, is, of course, a key factor in this. Sourcing the frame as close to home as possible can help to keep this carbon cost down.
It is worthwhile remembering, also, that the metal frame is a far more permanent addition, and if you take good care of it, it will be a one-off purchase. A plastic cover can also be a long-term purchase, and can last a long time if well cared for, but is far more likely than the metal frame to have to be replaced during the lifetime of the structure.
One polytunnel owner calculated that the cost of his polytunnel was approximately 1 tonne of CO2 emissions 2.To put this into context, one return flight across the Atlantic costs approximately 1.5 tonnes of CO2 per passenger. Approximately the same amount of CO2 would be emitted in the transportation of around 2.5 tonnes of food from Southern Spain to the UK or Ireland.
The Ecological Benefits of a Polytunnel
In order to work out whether there is a net ecological gain from the acquisition of a polytunnel, it is important to establish the net reduction in other carbon emissions that can be achieved through the use of the structure.
How a Polytunnel Can Reduce Your Carbon Footprint
By allowing you to grow food throughout the whole year, by increasing yields of produce, and by reducing losses to pests, disease or inclement weather, a polytunnel can allow individuals to reduce, or even eliminate, the need to buy food. The food we eat accounts for a huge proportion of our individual carbon footprints. Fossil fuels are used to grow much of the food available to buy in supermarkets, and additional carbon costs are involved in transporting food around the world.
Reducing Food Miles
We can reduce the carbon cost of the food we buy significantly by choosing organic, seasonal, locally grown produce. But the best way to reduce the carbon cost of the food we eat is to grow as much as possible on our own properties. A polytunnel not only makes it easier to do this, for more of the year, it also makes it possible to grow foods that it would not be possible to grow outdoors where we live – thereby reducing our desire for exotic foods grown in geographically distant locations.
We can reduce the carbon cost of the food we buy significantly by choosing organic, seasonal, locally grown produce. But the best way to reduce the carbon cost of the food we eat is to grow as much as possible on our own properties. A polytunnel not only makes it easier to do this, for more of the year, it also makes it possible to grow foods that it would not be possible to grow outdoors where we live – thereby reducing our desire for exotic foods grown in geographically distant locations.
The same polytunnel owner mentioned above is able to grow over 1 tonne of food in his polytunnel each year, thereby replacing food grown at high carbon cost, and transported at high carbon cost, to his area. The more food you are able to grow in your polytunnel, the more emissions can be reduced over time. Since significantly more food can be grown in a polytunnel than can be grown on a simple, outside plot, over time, these net reductions can begin to add up. The owner mentioned above calculated that the carbon ‘debt’ incurred by the polytunnel would be repaid within three years. While, of course, this repayment period would depend on how much you are able to grow, and how much food transported from elsewhere can be replaced, it seems clear that a polytunnel can be better than carbon neutral over the course of its lifetime.
Home Working Options
Another thing to note is that polytunnels can be used not only for growing food but for a range of other purposes. Some other uses for polytunnels could also help to reduce your carbon footprint. For example, a polytunnel may open up possibilities for you to work from home. This could reduce your carbon footprint by eliminating the need to commute to a workplace. This could be another piece in the puzzle of a more sustainable way of life.
How a Polytunnel Can Reduce Other Forms of Pollution
Carbon, and other greenhouse gases, are not the only form of environmental pollution that we should be concerned about in the modern world. Nor are they the only forms of pollution that buying a polytunnel can help you to reduce.
Modern mono-crop agriculture is one of the greatest polluters on our planet – a problem that most of us are complicit in creating. Pesticides, herbicides and synthetic fertilisers used on crops make their way into the water courses and degrade the planet’s fragile topsoils. They make their way into food chains and disrupt the world’s ecosystems and cycles.
By making it easier for individuals, communities and businesses to grow their own food locally and organically, a polytunnel can allow you to ‘opt out’ of the damaging systems of mass agriculture and thereby help to reduce these other forms of environmental pollution.
How a Polytunnel Can Help Reduce Waste
Another huge concern in our modern world is the problem of waste. Plastic ends up in our oceans and waterways, damaging vital ecosystems which we rely on for our very existence on this planet. Food waste and other items that end up in landfill are causing a problem that will endure for generations to come. Excessive consumption of goods and resources, and a lack of foresight about the waste we generate as a society, are creating a major issue for humanity and for our planet as a whole.
As individuals, we must all take responsibility for the waste we generate, and do our best to reduce waste as much as possible – ideally transitioning to a zero waste lifestyle. A polytunnel can help us immeasurably in achieving that goal.
Reducing Plastic Packaging
First of all, growing organic food in a polytunnel allows us to reduce the amount of food that we have to buy in supermarkets and other major shops. This means that we can reduce our need for, and in some cases eliminate our support for, the world of mass agriculture, which generates huge quantities of waste each year. What is more, since we will not have to buy as much food, a polytunnel can allow us to reduce the amount of plastic packaging that we bring into our homes each year.
Composting and Reusing Household Waste
Secondly, owning a polytunnel allows you to implement organic gardening practices which will make it easier to reduce the amount of waste for which you are responsible even further. Polytunnel gardeners and farmers can use compost food scraps and other organic waste to improve yield and to reduce waste leaving the property. Waste such as plastic food packaging can also be put to use in your polytunnel and there are a range of innovative ways in which you can reclaim and re-use items in a polytunnel which would otherwise end up in landfill.
Taking all of this into account, it seems clear that a polytunnel is of net ecological gain, and can definitely have a role to play in living a more eco-friendly and sustainable way of life.
1https://www.ecta.com/resources/Documents/Best%20Practices%20Guidelines/guideline_for_measuring_and_managing_co2.pdf
